Synthetic and Binding Studies on the Postulated Calcium Binding Site I of Calmodulin

Abstract

The synthesis of the dodecapeptide [sequence (20-31)] representing the hypothetical Ca binding site I of calmodulin by classical methods in solution is described. The interaction of this synthetic calmodulin fragment with Ca2+ ions was investigated by CD [circular dichroism] in water and in 98% trifluoroethanol solution. Ca2+ ions have no effect on the dichroic absorption of the dodecapeptide in aqueous solution in the wavelength range 200-250 nm. However, in 98% trifluoroethanol a linear variation of the CD properties was observed as a function of the .**GRAPHIC**. molar ratio. The CD results indicate the formation of a 1:1 Ca-dodecapeptide complex with a very high binding constant.